When automotive windows and side mirrors, bathroom mirrors and windows, etc. are exposed to moisture, their surfaces become cloud and so require frequent wiping, which is inconvenient. Accordingly, various measures are being taken to impart non-fogging property to the surfaces of such articles.
Heretofore, non-fogging layers designed to impart non-fogging to the surfaces of articles have typically included:
(i) layers caused to exhibit fogging-preventiveness by incorporating surface active agents in resins by kneading,
(ii) layers to which such inorganic salts as colloidal silica and phosphites are added to extend their non-fogging life, and
(iii) layers whose surfaces are made hydrophilic by modification of polymers such as saponification of acetyl cellulose.
However, a problem with the layers (i) and (ii) is that their non-fogging life is short due to the exudation of the surfactants, and the layers (iii) have low film strength during wetting so that when laid out, there are apt to be damaged and become degraded in terms of non-fogging.
In order to solve the above described problems of the prior art, we have already proposed a non-fogging sheet including a backing film and a non-fogging layer, characterized in that the non-fogging layer is obtained by exposure of a polymer and a hydrophilic monomer to electron beams for their crosslinking (e.g., Japanese Patent Laid-Open (Kokai) Publication Nos. 63-273668, 63-251401, 63-258905, 63-258904 and 63-278840).
Incidentally, non-fogging sheets including relatively thick, non-fogging layers (hydrophilic films) have recently been in great demand due to requirement for non-fogging to be much more improved and retained over a much longer period of time. However, it has now been found that when it is intended to form thicker non-fogging layers with a solvent-containing coating solution, not only do solvent residues pose another problem, but the resulting non-fogging layers suffer surface roughening as well, thus making them unsuitable for non-fogging sheets to be applied over mirrors or windowpanes.